PROVIDENCE — No one stepped forward to help the police after a 12-year-old girl was murdered and three women were wounded last month during a party at the Hartford Park housing project on the night before...

By W. Zachary Malinowski and Amanda Milkovits

PROVIDENCE — No one stepped forward to help the police after a 12-year-old girl was murdered and three women were wounded last month during a party at the Hartford Park housing project on the night before Father’s Day.

The terrified survivors of the high school graduation party said they saw a masked gunman casually fire upon them just before midnight, killing young Aynis Vargas and leaving without a word. But despite pleas from the Providence police, the mayor and the Vargas family, witnesses refused to talk.

An affidavit in support of a search warrant shows that Hartford Park’s video surveillance system played a key role, showing a distinctive-looking minivan being driven “suspiciously” in the area the night of June 15. The video also captured a masked gunman heading to a row of apartments at 256 Hartford Ave., where the party was running late.

Another tool was the cellphone records of the minivan’s owner, a gang member from South Providence, and text messages he sent to his girlfriend before and after the murder.

On July 17, the police arrested two Harriet Street gang members — Ricardo Vasquez, 20, who police say was driving the van, and Branden Castro, 21, who police say fired the shots — charging them with the murder of Aynis and the wounding of the three women. Police Chief Hugh T. Clements Jr. said the case remains under investigation and more arrests are expected.

This was the second time in three weeks that a high-profile murder investigation in southern New England was advanced through the use of video surveillance and cellphone records. On June 26, North Attleboro police and Massachusetts State Police charged Aaron Hernandez, the former All-Pro tight end for the New England Patriots, with first-degree murder in the execution-style slaying of Odin L. Lloyd of Boston near Hernandez’s house in North Attleboro.

Steven M. Paré, Providence public safety commissioner, said investigators are relying more on cellphones, computers and social media to solve cases, especially during a time when increasing numbers of witnesses are reluctant to cooperate with the police.

“It’s routine today,” he said. “There is evidence on cellphones and laptops. We seize them for potential evidence.”

Sharon Fray-Witzer, a professor at Northeastern University’s School of Criminology and Criminal Justice, said law enforcement agencies, like the rest of society, understand that technology can help make arrests.

“My sense is that police officers will seek whatever information they can get to crack a case, that they are presented with ever more options by our use of technology to make our lives easier and safer, and that the courts are typically slow to respond to the legal challenges that changes in technology present,” she wrote in an email. “The courts are still sorting out how far police can go in searching phones and computer hard drives, and likely will be for some time.”

In the Vargas case, the Providence police got more than 20 court-authorized warrants to search video recordings and cellphones, while investigators in Massachusetts had judges sign at least 11 warrants to get similar information in the Hernandez murder probe.

Four hours after the mass shooting at Hartford Park on the city’s west side, police were still at the scene when a young man from Elmwood Avenue on the south side called to report that his minivan had been stolen.

The investigators had reviewed the video surveillance footage from that night and searched for clues. The video didn’t capture the actual shooting, but it showed the gunman walking across Hartford Avenue toward the row of apartments at 256 Hartford Ave., where the party was going on.

And, it showed a minivan driving oddly around the public housing apartments — making illegal U-turns, pulling in and out of parking lots, and finally backing into a parking space near the murder scene.

The license plate was hard to read, but the van was distinctive: It had a different color passenger-side rear door and black tape covering a broken rear passenger window.

Officers had been told to be on the lookout for the minivan when Patrolman Jerome Lynch showed up June 16 at Ricardo Vasquez’s residence on Elmwood Avenue to take a report of a stolen vehicle.

Vasquez told him that someone took his 2001 Nissan Quest. It was silver with a dark green sliding door, and a bag covering a broken rear window.

It sounded a lot like the minivan wanted in the murders. Lynch recognized the description, said Chief Clements.

That afternoon, Vasquez told police that he found his stolen minivan, parked outside 86 Julian St., in the Manton neighborhood — the home turf of a street gang feuding with a gang in Hartford Park, Clements said.

But Vasquez is a member of the Harriet Street gang, which is also warring with Hartford Park.

Investigators quickly determined that the shooting was part of an ongoing dispute between gangs from Harriet Street and Hartford Park. The police say that there are about 2,300 gang members in the city with “15 or 16 active gangs.”

Aynis and the three women shot had nothing to do with either gang, but the police theorize that the Harriet Street gang was simply looking to send a message and open fire on anyone in the Hartford Park housing project.

Police believed that Vasquez was trying to use the “stolen vehicle” ruse to distance himself from the shooting.

Vasquez told Detectives Frank Villella and William Mattera that someone had smashed his van’s window the previous afternoon. He said he spent the night of June 15 with his girlfriend, Dignailis Estrella, dropped her off at 9:30 p.m. and then went home to bed a half-hour later, according to an affidavit. He told police he found out his minivan was missing at 4 a.m. the next day.

The police showed Vasquez the video of the minivan in the Hartford projects, and he said it was his van — and that he didn’t let anyone else use it. He also said he had his cellphone with him that night, when the shooting occurred.

Detective Theodore Michael drew a search warrant for Vasquez’s cellphone records, which told the story that the young man omitted.

Vasquez and his girlfriend were texting each other from 9 p.m. to 3 a.m. — hours before and after the fatal shooting.

Two hours before, Vasquez texted: “I’m OK, jus scheming real quick.” Estrella told him to be careful, and he texted back: “I will im not stupid baby. I’m ready to lay suttin flat.” Police believe he meant he was planning an act of violence.

About two hours after the mass shooting, Vasquez texted his girlfriend again: “[Expletive] went sour bae, we needa talk. … [Expletive] went Down & There were 3 hit and one down … * for good.”

To police, that meant someone had died.

According to the affidavit, Vasquez texted: “Ima hide my car and report it stolen.” She asked: “Theirs no gun powder or finger prints in the van?”

Vasquez responded: “Na Ntn happened from the car.”

Two hours later, he called police about his stolen van.

The cellphone records revealed the path that Vasquez took that night. Although he’d claimed to be home sleeping about three miles from the homicide scene, the cell tower records showed his phone was a half-mile away from Hartford Park just 11 minutes before the shooting.

Vazquez was charged with first-degree murder, conspiracy — plus obstruction of justice and filing a false police report. His friend Castro is charged with murder and assault with a dangerous weapon. Both face life in prison.

Technology also played a key role in the Aaron Hernandez investigation.

Investigators from the Massachusetts State Police and the North Attleboro police reviewed cellphone text messages between Hernandez, 23, and Lloyd, a 27-year-old semipro football player who was dating the sister of Hernandez’ live-in girlfriend. The messages began shortly after midnight, on June 17, and continued until his death several hours later.

There also was texting between Hernandez and Carlos A. Ortiz, 27, and Ernest Wallace, 41, who are accused of being in the rental car with Lloyd and at an industrial area in North Attleboro where Hernandez is alleged to have shot Lloyd five times with a .45-caliber handgun less than one-half mile from Hernandez’s home.

Lloyd’s bullet-ridden body had a cellphone tucked into a front pocket of his sweatshirt. Investigators seized the phone and discovered that he had sent a text message to Hernandez at 12:22 a.m., about three hours before Lloyd was murdered.

“We still on?” Lloyd texted.

The next day, June 18, investigators got a warrant to search Hernandez’s cellphone for “all data files including call logs, text messages, image files, videos, voice mails, contact lists and other data files that can reasonably be related to the death of Odin Lloyd.”

On that same day, investigators obtained a second warrant to seize video from the surveillance system at Hernandez’s house.

The murder investigation quickly gained steam as detectives gathered evidence that tracked Hernandez, Ortiz, Wallace and Lloyd on the morning of the murder. They hit the jackpot with text messages, GPS tracking through Hernandez’s cellphone and other video surveillance footage.

Hernandez was arrested and charged with murder on June 26. At his arraignment, William M. McCauley, first assistant district attorney for Bristol County, said the former football star began plotting Lloyd’s murder on Sunday, June 16. Authorities have said Hernandez was angry about people that Lloyd had been talking with at a Boston nightclub.